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(gawk.info)Calling Built-in

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Calling Built-in Functions
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   To call one of `awk''s built-in functions, write the name of the
function followed by arguments in parentheses.  For example, `atan2(y +
z, 1)' is a call to the function `atan2', and has two arguments.

   Whitespace is ignored between the built-in function name and the
open parenthesis, and it is good practice to avoid using whitespace
there.  User-defined functions do not permit whitespace in this way, and
it is easier to avoid mistakes by following a simple convention that
always works--no whitespace after a function name.

   Each built-in function accepts a certain number of arguments.  In
some cases, arguments can be omitted. The defaults for omitted
arguments vary from function to function and are described under the
individual functions.  In some `awk' implementations, extra arguments
given to built-in functions are ignored.  However, in `gawk', it is a
fatal error to give extra arguments to a built-in function.

   When a function is called, expressions that create the function's
actual parameters are evaluated completely before the call is performed.
For example, in the following code fragment:

     i = 4
     j = sqrt(i++)

the variable `i' is incremented to the value five before `sqrt' is
called with a value of four for its actual parameter.  The order of
evaluation of the expressions used for the function's parameters is
undefined.  Thus, avoid writing programs that assume that parameters
are evaluated from left to right or from right to left.  For example:

     i = 5
     j = atan2(i++, i *= 2)

   If the order of evaluation is left to right, then `i' first becomes
six, and then 12, and `atan2' is called with the two arguments 6 and
12.  But if the order of evaluation is right to left, `i' first becomes
10, then 11, and `atan2' is called with the two arguments 11 and 10.